1. Field of Invention
This invention relates to a system for measuring the surface densities, thickness, and the like, of sheet materials, such as paper, plastic, rubber, etc.; and more particularly, to improvements in the distribution functions of a microprocessor in a sensor control/computation unit of a sensor. This invention also relates to a man-machine interface unit used in a control system for a paper manufacturing or coating machine; and more particularly, to improvements therein which produce legible display even when the number of final control elements is greatly increased.
2. Description of the Prior Art
In the paper making industry, basis weight, moisture content, thickness, gloss, color, etc., are measured to assess paper quality. In order to control paper quality to targeted values, a sheet measurement and control system is used. An example of such system is disclosed in Japanese Unexamined Patent Application Hei 8-61,942 (1996).
FIG. 1 shows a sheet measurement control system, wherein measurement frame 30 is a rectangular frame spanned in a cross direction (which is defined herein as being in a direction which is transverse to the travel direction, labeled herein as "machine direction") of sheet 40. Sensor head 32 is caused to move back and forth (see arrow) along this frame 30 on the front and rear surfaces of the sheet 40 to provide reciprocal scanning of sheet 40. Since a sheet manufacturing machine continuously manufactures and moves sheet 40 in the machine direction, the running locus of the sensor head 32 above the sheet 40 shows a zig zag pattern or trace. The Measurement Frame and Sensor Management Unit 34 implements data processing and computation using the measured sensor signals and the measured sensor positions in the cross direction. In this sheet measurement and control system, data are processed to separate the computed data into a component in the machine direction and another component in the cross direction.
Man-Machine Interface 52 is disposed in a location independent of measurement frame 30 to enable an operator to more conveniently and easily observe the running state of the sheet manufacturing system. For example, the data component in the cross direction of the measured value computed with Measurement Frame and Sensor Management Unit 34 is called a "profile". The profile is displayed so that the operator can monitor the uniformity of the sheet quality in the cross direction.
FIG. 2 shows a conventional small scale measurement and control system, wherein three types of units, sensors 10. sensor processor 14, and communication processor 16 are mounted in sensor head 32. Two different types of sensors 10, for example,are mounted in sensor head 32. However, two similar types of sensors can also be used. For example, in a basis weight meter, if promethium-147 (.sup.147 Pm) is used as a Beta source, measurement accuracy is good but the measurement range is limited to 0 to 100 g/cm.sup.2. On the other hand, if strontium-90 (.sup.90 Sr) is used as the beta source, measurement accuracy is not as good, but the measurement range is extended to 0 to 2000 g/cm.sup.2, that is by about one decade or more. Thus, when paper of large basis weight and paper of small basis weight have to be manufactured using the same paper making process and changing the recipe, this can be done by switching the beta source between the promethium-147 and the strontium-90.
A sensor processor 14 is provided for each sensor 10 and corrective computation is carried out on the analog output signals from each of the sensors to compute the instantaneous measured values. The computed instantanous measured values are then sent consecutively to a communication processor 16. Communication processor 16 is also disposed in sensor head 32 and is connected to each sensor processor 14 on a 1 to N basis, and exchanges data with each sensor processor 14 by direct access corresponding to requests from a supervisory computer. For example, the instantaneous measured values computed each sensor processor 14 are stored serially with time and the resulting time series data are sent to operation processor 36 at the request of operation processor 36.
The operation processor 36 is disposed on the measurement frame 30. It creates profiles representing sheet quality in the cross direction by combining the time series instantaneous measured value data, sent from communication processor 16, with the positional data of sensor head 32 in the cross direction. The processor 36 also eliminates measurement noise components using, for example, a smoothing process. The operation processor 36 is connected to communication processor 16 with signal cable 24. In addition, the man-machine interface 52 fetches required data by accessing the operation processor 36 and displays the data so that an operator can conveniently and easily observe the running state of the sheet manufacturing system.
In the conventional system, analog signals outputted from sensor 10 are delivered to sensor processor 14 and then to communication processor 16. By the operations discussed above, the measured values are transmitted ultimately from sensor 10 to operation processor 36. The signal cable 24 is suitable for digital high speed communication.
Furthermore, in order to show paper quality, a profile display unit, such as disclosed in Japan Unexamined UM Sho 63/175,198 (1988) may be used. FIG. 3 shows a display screen of the profile data, wherein line (A) shows profiles of measured values PV and set values SV; line (B) shows a profile of manipulated variable MV; and line (C) shows a position cursor. The measured values PV and the set values SV are displayed with line segment graphs, and the manipulated variables MV are displayed with bar graphs. The horizontal axis shows the positions in the cross direction. The position cursor is displayed under the MV profile display and also serves as an input device to specify a final control element selected from a plurality of final control elements.
However, since several sets of sensors 10 and corresponding sensor processors 14 are fed into communication processor 16, it is also necessary for the communication processor 16 to be changed when the type of sensor 10 is changed. The work involved in replacing sensor 10 is time consuming and complex. In addition, only a single sensor 10 can be mounted on the sensor head 32 in some application In such applications, since the communication processor 16 has to handle a plurality of sensors 10, the cost is increased.
Furthermore, recently, CP control of the basis weight has been used, wherein the inlet pulp concentration is locally adjusted by opening and closing multiple valves arranged in the cross direction of the paper sheet. Compared with other conventional basis weight control that adjusts the slice bolt, in the CP control system, the number of manipulated variables MV is increased considerably. For example, the number of valves might reach several hundred in one case. This results in the manipulated variables being displayed in a profile data display close together, thereby making identification by the cursor more difficult.